This application generally relates to balloon catheters. In this regard, various types of balloon catheters are routinely employed in medical procedures. Typically, balloon catheters consist of elongate, thin-walled tubular catheter assemblies with an inflatable balloon attached at the distal end.
Balloon catheters are commonly used to dilate or remove constrictions, or to deliver and deploy other devices within bodily conduits. In the treatment of constricted conduits, the balloon catheter is inserted within the patient and navigated through the conduit (such as a blood vessel) to the site of blockage. The balloon at the distal end of the catheter is then inflated, causing the balloon to increase in diameter until the desired therapeutic result is achieved. Once the blockage is opened, the balloon is deflated and removed from the patient.
In a similar fashion, devices such as stents are typically secured onto the distal ends of balloon catheters, the catheters being used to deliver the stent to the site of a blockage. Once at the desired location, the underlying balloon is inflated, causing the stent to increase in diameter and thus remodel and support the tissue, which constitutes the blockage within the bodily conduit. Once the therapeutic result is achieved the balloon is deflated and removed from the patient, leaving the stent implanted.
Balloon catheters may employ various balloon materials depending on the application for which they are used. For example, embolectomy balloon catheters utilize elastomeric balloon materials such as latex or silicone because, in such procedures, there is no need for the use of high inflation pressures. Angioplasty balloon catheters, on the other hand, utilize relatively inelastic materials such as polyester or nylon because in such procedures the application of high inflation pressure is often required.
Elastomeric and inelastic balloon materials each have advantages and drawbacks. While elastomeric materials are generally soft and conformable, they lack strength and exhibit continuous diameter growth with the application of increasing inflation pressure until rupture occurs. Elastomeric balloon materials are referred to as compliant. Inelastic balloon materials have very predictable diameter growth characteristics, and distend very little beyond their intended diameter with the application of increasing inflation pressure. Inelastic balloon materials are referred to as non-compliant or semi-compliant depending on their stiffness.
Due to their stiffness, inelastic balloon materials are not soft and conformable. Balloons made of these materials, such as angioplasty balloons, are carefully wrapped into a small cross-sectional configuration prior to introduction into the patient. During inflation, the balloons unwrap and assume their intended diameters. During subsequent deflation, however, the balloons do not return to their initial small cross-sectional state.
Angioplasty balloons are often difficult to maneuver through tortuous bodily conduits, posing a challenge in the treatment of blockages within small conduits such as within the coronary vasculature or the neurovasculature. Further, when inflated within a curved conduit, such balloons tend to straighten the conduit because of their lack of conformability. This straightening can result in localized trauma.
The delivery of devices such as stents via angioplasty balloon catheters can be problematic due to inadequate securement of the stent onto the balloon. The inelastic materials do not provide adequate engagement to the stent, leaving the stent prone to slipping along the length or completely off of the balloon. Also, because the inelastic materials are essentially non-compressible, the edges of a stent, when mounted onto a balloon made of such materials, are exposed and vulnerable to being damaged during navigation through narrowed tortuous conduits.
In addition to the drawbacks mentioned above, there are complications associated with the mechanics of folded balloons. As described, angioplasty balloons are typically folded or wrapped about the catheters to which they are attached. During use, the balloons unfold at very low pressure. In the presence of an obstruction within a conduit, particularly if the obstruction is centered within the length of the balloon, such balloons tend to unfold very quickly at the ends where diameter growth is unimpeded, forming an hourglass shape. As the balloon is inflated to greater pressures, the obstructive tissue is remodeled toward the center of the balloon length, creating a densified lesion and a generally insufficient vessel inner diameter. Similar mechanics may occur during inflation of a stent, particularly if the length of the stent is not carefully matched to the length of the balloon.
In many cases, blockages occur close to the junction of two conduits. In such situations, particularly if the lesion is located at one end of the balloon, the mechanics described above, rather than densifying the obstructive tissue towards the center of the balloon, redistribute the occlusive tissue into the junction between the two conduits, thus compromising the junction and creating an obstruction within the branching conduit.
Another complication of balloon angioplasty and stenting is the formation of emboli. Embolic episodes occurring in various anatomical locations, particularly the brain can result in potentially debilitating outcomes or even death.